Overview of some current 12AX7 tubes

[mamberg]

I have read about a 'hardness' rating of tubes by some of the NOS dealers online.

If I understand correctly (and am not being fed a line of BS), a hardness rating of 4-6 is standard breakup, 7-9 is a late breaking tube (meaning it stays clean longer-till a higher output), and 2-3 is a tube that goes into distortion sooner.

Could that be the difference that soulcrusher is hearing with the JJ's having a louder output, but not seeming to be a higher gain tube?? that they ARE a higher gain, but also a higher hardness rating? -and therefore not going into distortion as soon?

I am reading alot about NOS tubes (and tested pulls) as I have experienced a BIG improvement in tone when switching from new production to old production.

I love my modded VJr. and Tiny Terror clone as I can actually afford to buy an assortment of tubes to try out in them. More info is always welcome.

thanks

[VanR]

After reading this thread I thought I would do a little taste test in my ax84.com High Octane. And I hate to say it but those EH 12AX7's just sound good. Unfortunately I dropped and broke the only one I had while doing the test. I've always been a Chinese 12AX7 man. And I still think they are good sounding consistent and reliable 12AX7, but in this amp the EH just sounds better. Even better than the RCA 12AX7A I was running in there. The EH is just smooth in this amp and there is none of the harshness I've been trying to dial out of the amp for years.
I tried the
RCA 12AX7A
Chinese 9th 12AX7
Chinese 8th 12AX7
EH 12AX7
Now I'm thinking I should try a JJ ECC83 if I can get my hands on one. I hear they are darker and smoother than most. Maybe they will tame the harshness in this amp.
Of course this is just this one amp so YMMV. I still run RCA's in all my other amps.

[Soulcrusher_X]

I have read about a 'hardness' rating of tubes by some of the NOS dealers online. If I understand correctly (and am not being fed a line of BS), a hardness rating of 4-6 is standard breakup, 7-9 is a late breaking tube (meaning it stays clean longer-till a higher output), and 2-3 is a tube that goes into distortion sooner. Could that be the difference that soulcrusher is hearing with the JJ's having a louder output, but not seeming to be a higher gain tube?? that they ARE a higher gain, but also a higher hardness rating? -and therefore not going into distortion as soon? I am reading alot about NOS tubes (and tested pulls) as I have experienced a BIG improvement in tone when switching from new production to old production. I love my modded VJr. and Tiny Terror clone as I can actually afford to buy an assortment of tubes to try out in them. More info is always welcome. thanks

 

 

I think that the gain rating is more closely related to it's output than what most people think of when they refer to "gain". A tube can have a high output, but not a gritty distorted sound, which is what most people think gain is.

 

I could just be talking out of my tubes though.

[Soulcrusher_X]

After reading this thread I thought I would do a little taste test in my ax84.com High Octane. And I hate to say it but those EH 12AX7's just sound good. Unfortunately I dropped and broke the only one I had while doing the test. I've always been a Chinese 12AX7 man. And I still think they are good sounding consistent and reliable 12AX7, but in this amp the EH just sounds better. Even better than the RCA 12AX7A I was running in there. The EH is just smooth in this amp and there is none of the harshness I've been trying to dial out of the amp for years. I tried the RCA 12AX7A Chinese 9th 12AX7 Chinese 8th 12AX7 EH 12AX7 Now I'm thinking I should try a JJ ECC83 if I can get my hands on one. I hear they are darker and smoother than most. Maybe they will tame the harshness in this amp. Of course this is just this one amp so YMMV. I still run RCA's in all my other amps.

 

 

I like the EH 12AX7 in my MKIII a lot. I use two EH, two C9s and an LPS as the PI tube.

[Sn8ke]

Myles, are you God?

What are the best 12AX7's to pair with a balanced set of JJ KT77's? Right now I have some high gain JJ's which give me a good overdrive but loses a ton of brightness (good thing my clean channel has a bright boost switch or I wouldn't be able to survive)

Anyway, thanks for all your time you've shared on this subject, your knowledge is appreciated!!

[Myles]

I have read about a 'hardness' rating of tubes by some of the NOS dealers online. If I understand correctly (and am not being fed a line of BS), a hardness rating of 4-6 is standard breakup, 7-9 is a late breaking tube (meaning it stays clean longer-till a higher output), and 2-3 is a tube that goes into distortion sooner. Could that be the difference that soulcrusher is hearing with the JJ's having a louder output, but not seeming to be a higher gain tube?? that they ARE a higher gain, but also a higher hardness rating? -and therefore not going into distortion as soon? I am reading alot about NOS tubes (and tested pulls) as I have experienced a BIG improvement in tone when switching from new production to old production. I love my modded VJr. and Tiny Terror clone as I can actually afford to buy an assortment of tubes to try out in them. More info is always welcome. thanks

 

 

Go here for some info on rating and how it also effects power a little which is shown on the chart on the page at - http://www.guitaramplifierblueprinting.com/Rating.html

[Myles]

After reading this thread I thought I would do a little taste test in my ax84.com High Octane. And I hate to say it but those EH 12AX7's just sound good. Unfortunately I dropped and broke the only one I had while doing the test. I've always been a Chinese 12AX7 man. And I still think they are good sounding consistent and reliable 12AX7, but in this amp the EH just sounds better. Even better than the RCA 12AX7A I was running in there. The EH is just smooth in this amp and there is none of the harshness I've been trying to dial out of the amp for years. I tried the RCA 12AX7A Chinese 9th 12AX7 Chinese 8th 12AX7 EH 12AX7 Now I'm thinking I should try a JJ ECC83 if I can get my hands on one. I hear they are darker and smoother than most. Maybe they will tame the harshness in this amp. Of course this is just this one amp so YMMV. I still run RCA's in all my other amps.

 

 

You cannot compare tubes in this way other than figuring out what you prefer in the amp from a specific single tube standpoint. If you have a nice Gen8 and a crappy Gen9 as an example where one meets spec and the other is shot or junk then you may prefer one over the other.

 

To accurately compare tubes of various types use tubes that all have the same gain, plate current output, transconductance. Otherwise you are trying to taste test two oranges ... Florida vs California, where one is fresh and the other is rotten.

[Myles]

I think that the gain rating is more closely related to it's output than what most people think of when they refer to "gain". A tube can have a high output, but not a gritty distorted sound, which is what most people think gain is. I could just be talking out of my tubes though.

 

 

Gain and output are two very different things. It is like torque and horsepower are different things.

[Myles]

Myles, are you God? What are the best 12AX7's to pair with a balanced set of JJ KT77's? Right now I have some high gain JJ's which give me a good overdrive but loses a ton of brightness (good thing my clean channel has a bright boost switch or I wouldn't be able to survive) Anyway, thanks for all your time you've shared on this subject, your knowledge is appreciated!!

 

 

God? No ... just an old guy that grew up in the sixties who is stuck in 66-69 San Francisco acid rock and blues .... a guy that has been married three times and shot twice, been in two airplane crashes and one parachuting accident.

 

But ... as to you question .... there is no right answer as it is personal taste. The JJ KT77 is a cool tube. I like them in the 65amps Royal Alberts that Keith Urban plays and in Carl Verheyen's SRZ-65 that he uses in Europe we have the KT77 in that amp (E34LS in the USA SRZ-65). In Carl's amp in use a 12AX7R2 (Sovtek 12AX7LPS) in V1 and the phase inverter but that was just his personal pick after a lot of experimentation. If things are still stock in Keith's amps he may have the Ei 7025 in V1 as Dan at 65amps has a stash of those and likes them a lot. So ... in the end there is no "right" setup for a given power tube and preamp tube.

 

Experiment and use your ears is my best advice.

 

If you are ever in L.A. I would be happy to sit behind your amp as you play and swap a bunch of stuff in and out to dial things in without you needing to have a pile of different preamp tubes at no charge.

[Soulcrusher_X]

Gain and output are two very different things. It is like torque and horsepower are different things.

 

 

 

I don't want to drag you out in a huge, long post, but is there a somewhat simple answer to the difference between gain and output?

[Myles]

I don't want to drag you out in a huge, long post, but is there a somewhat simple answer to the difference between gain and output?

 

 

That would be something where you would need a base understanding of electronics / tube stuff.

 

Output is generally the plate current output. Gain is generally how much the input signal is amplified from what comes in to what goes out. A gain of 100 means the signal is amplified 100 times in one gain stage on one side of a spec tube. But .... just like electricity, you can touch 500,000 volts from one of those machines that makes your hair stand on end as there is no current or amperage to speak of. But 12 volts at 50 amps as in a car battery will clean your clock.

 

So ... even with a gain of 100 if there is not the output current then the signal will have a much more difficult time pushing though a messy and complex circuit design. In complex multi gain stage amps with a lot of pots and junk in the signal path I take that into consideration when selecting tubes and try to find ones with proper gain but also good plate current output. Plate current output is also very critical to me for phase inverter use, especially in 6L6 amps as these are harder to drive than EL84s as an example. When you have 6 6L6 tubes such as a Mesa triple recto you better have decent current drive in that phase inverter! An Ampeg SVT used two phase inverters, and 12AU7s at that to push the 6146 or 6550 output sextet as an example.

 

Fender blackface and silverface amps are not as critical as they use a 12AT7 in the phase inverter position which has almost ten times the plate current output than a 12AX7 has.

[Elric]

I don't want to drag you out in a huge, long post, but is there a somewhat simple answer to the difference between gain and output?

A dirt simple working definition of gain is ratio of output to input for some factor. I.e. if at some instant in time a 10V input to a ckt gives you a 20V output, you have a voltage gain of "2" at that instant from that circuit. Since it is just an output to input ratio, there are an arbitrary number of different types of gain that can be defined or measured depending on what you are putting in/out. I.e. current gain, voltage gain, etc and the value will depend on what signal you are amplifying, ie. DC gain versus AC, etc. As well as the signal's content (i.e. frequency spectrum, etc).

As you'd guess by the heated nature of some of the discussion, when you dig into it, measuring it reliably/consistently is not quite as trivial as it seems, since, as noted gain can vary with signal content and operating conditions and since we may or may not be concerned with more than one type of gain at any given time it's an easy thing to confuse and/or argue about.

[Myles]

A dirt simple working definition of gain is ratio of output to input for some factor. I.e. if at some instant in time a 10V input to a ckt gives you a 20V output, you have a voltage gain of "2" at that instant from that circuit. Since it is just an output to input ratio, there are an arbitrary number of different types of gain that can be defined or measured depending on what you are putting in/out. I.e. current gain, voltage gain, etc and the value will depend on what signal you are amplifying, ie. DC gain versus AC, etc. As well as the signal's content (i.e. frequency spectrum, etc). As you'd guess by the heated nature of some of the discussion, when you dig into it, measuring it reliably/consistently is not quite as trivial as it seems, since, as noted gain can vary with signal content and operating conditions and since we may or may not be concerned with more than one type of gain at any given time it's an easy thing to confuse and/or argue about.

Great point.

"Gain" is dependant on many things, circuit design for one.

As an example, when a tube factory makes a "12AX7" the spec is that at 250 plate volts with 2 volt bias the tube should have 62.5K of plate resistance and this would yield a gain of 100. The current output if all things are right is 1.2 milliamps and the TC is 1600.

But there is a second spec at 100 plate volts with a 1 volt bias then the gain is still 100 but the plate resistance is 80K, the current output 0.5mA and the TC 1250 for a spec tube.

Gains remains the same as the target and expectations but the other factors have changed quite a bit.

Most spec sheets show the info at 250 plate volts with a 2 volt bias but most spec sheet simply copy spec and print them on their spec sheets. This is the intended result they try to reproduce. In the past they were very close. Today being over 50% of spec is quite common more often than not. That is why I publish test results from each batch of tubes I test so the actual results are out there for folks. Some of the vendors see these results and actually contact us for returns of tested stuff and the data sheets so they can make an attempt to fix things.

[Soulcrusher_X]

Cool! Thanks for the info, guys. I've really been wanting to get more into tube amp theory and design, as I think it would be a trip to build and design an amp, starting with a predesigned kit. Knowing more about those little bottles would sure help out a lot when it comes to trying out my own design and/or troubleshooting.

[pepperduck]

so i changed out the v1 preamp tube on my orange from a 12AX7 to a 12AY7 and the difference is unbelievable.

 

also, thanks to Myles for sending me to that NOS tube distributor.

[Myles]

so i changed out the v1 preamp tube on my orange from a 12AX7 to a 12AY7 and the difference is unbelievable. also, thanks to Myles for sending me to that NOS tube distributor.

 

 

Happy playing!